I've been listening to my newly purchased HD-669s for the last three days and they are just ridiculously nice, especially for the price.
They cost me € 29,- which is around 40 bucks.

Build quality is perfectly fine and they come with a 1m and a 3m detachable cable which is really handy if you use them with portable players. My Sansas and Cowons drive these phones to pretty loud levels and sound excellent through them.

While closed-back they have a pretty expansive (in depth and with) soundstage which is truly 3D and not just left right. Music that tends to sound somewhat congested at times on a lot of other phones (e.g. some Dreamtheater stuff when they all go into Def-Con 3 mode at once) has exceptional clarity and definition and it's like there is more space between the different instruments spatially and sonically if that makes any sense.

Highs are nicely extended, these have exceptional clarity and definition, mids are complex and natural and neither too forward nor recessed while bass is natural in that it represents what's on the recording. If there is a lot of bass it's slammin' but it's not artificially boosted in any way.

Excellent balance is the keyword here and you realize how 'close to live' these Superlux sound.

To find an analogy it's a bit like being cured from shortsightedness all of a sudden and realizing how much you have missed out not seeing entirely clearly.

They are not better than the AKG K601s but almost on par with them while providing a closed-back construction with much better isolaton and they can be used without an amplifier with an mp3-player and sound great while the K601s need an amp for that.

They clearly trump my Sony MDR-V6 and Sony MDR-V700 headphones which are both closed back and are studio-monitors and DJ-headphones respectively. These are nice headphones but the HD-669 eats them for lunch on soundstage, instrument separation and placement and overall balance and detail reproduction.

Isolation is very decent and comfort is good, the clamping force is a bit on the tight side initially but they loosen up over time and you can bend the two frame wires gently to make them fit more comfortably if needed.

The design is kind of minimalist and a bit on the Bauhaus side which is perfectly fine for me (all black so what's not to like ), they are pretty humongous in size (almost as big as my AKG 601s) but rather lightweight. If you dare to wear them outside be prepared to be stared and/or laughed at by the dumbed-down and braindead as they do look a bit like being part of some ancient austronauts helmet.

Here are some pics from the website I purchased them from:

Overall I couldn't be more pleased with them, I was expecting something good but they have exceeded my expectations. Excellent value for money.

Even for that price they are worth it, Superlux makes headphones for many of the big name brands and it really shows. They also make a Beyerdynamic DT770 clone called HD-660 which is also supposed to be pretty good. One guy compared them to his 250 Ohm DT770 and said there were only marginal differences, the HD-660 sounded a bit more 'fresh' which was to be expected as the DT770s had been in use for a number of years but the sound signature is said to be extremely close.

There's a shop in town that sells Superlux headphones but they won't let anyone audition them. The price is pretty steep compared to online prices though. My main concern with the superluxes would be their durability.

The plastic things that look like bones just a little above the cups don't look too good...

The plastic things that look like bones just a little above the cups don't look too good...

Probably looks like that in the pictures but these 'bones' are well-made and far from being flimsy. Can't really comment on their long-term durability yet but they are solidly built and everything is tight and no creaky, thin plastic parts at all.